RFR(M): 8130847: Cloned object's fields observed as null after C2 escape analysis

Roland Westrelin roland.westrelin at oracle.com
Tue Jul 28 18:26:33 UTC 2015

Thanks for looking at this, Vladimir.

> The next change puzzles me:
> -         if (!call->may_modify(tinst, phase)) {
> +         if (call->may_modify(tinst, phase)) {
> -           mem = call->in(TypeFunc::Memory);
> +           assert(call->is_ArrayCopy(), "ArrayCopy is the only call node that doesn't make allocation escape");
> Why only ArrayCopy? I think it is most of calls. What set of tests you ran?

I ran:

java/lang, java/util, compiler, closed, runtime, gc jtreg tests
nsk.stress, vm.compiler, vm.regression, nsk.regression, nsk.monitoring from ute

I’m not sure if I did CTW or not but I can if you think it makes sense.

Aren’t arguments of calls marked as ArgEscape so an object that is an argument to a call cannot be scalar replaced?

> Methods naming is confusing. membar_for_arraycopy() does not check for membar but for calls which can modify. handle_arraycopy() could be make_arraycopy_load().
> Add explicit check:
> && strcmp(_name, "unsafe_arraycopy") != 0)

Thanks for the suggestions. I’ll make the suggested changes.


> Thanks,
> Vladimir
> On 7/28/15 7:05 AM, Roland Westrelin wrote:
>> http://cr.openjdk.java.net/~roland/8130847/webrev.00/
>> When an allocation which is the destination of an ArrayCopyNode is eliminated, field’s values recorded at a safepoint (to reallocate the object) do not take the ArrayCopyNode into account at all and the effect or the ArrayCopyNode is lost on a deoptimization. This fix records values from the source of the ArrayCopyNode, emitting new loads if necessary.
>> I also use the opportunity to pin the loads generated in LoadNode::can_see_arraycopy_value() because they depend on all checks that validate the array copy and not only on the check that immediately dominates.
>> Roland.

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